Capacitance sensor for detecting a charge voltage of a multi-capacitor circuit

ABSTRACT

A capacitance sensor includes a first charging voltage detector configured to detect a change in a voltage loaded into a first capacitor between an electrode and a ground terminal a second charging voltage detector configured to detect a change in a voltage loaded into a second capacitor among a plurality of electrodes and a determiner configured to generate a determination signal based on a detection voltage transmitted from each of the first charging voltage detector and second charging voltage detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2008-059779, filed on Mar. 10,2008, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a capacitance sensorwhich transmits a detection signal indicating that a change in a chargeloaded into a capacitor has been detected.

BACKGROUND

A capacitance sensor used in a touch sensor, by detecting a change in acapacitance among a plurality of electrodes with a detection circuit,can detect a touch of an object to be detected such as a human body orthe like.

FIG. 18 illustrates one example of a detection principle of thecapacitance sensor. As detection elements, two electrodes 1 a and 1 bare spaced a certain distance apart on a substantially identical plane,and the electrodes 1 a and 1 b are covered with an insulator 2. For theelectrodes 1 a and 1 b, as illustrated in FIG. 19, for example, theelectrode 1 b may be laid out around the electrode 1 a, and furthermore,a guard member 3 may be laid out around the electrode 1 b, keeping theelectrodes in electrical isolation from another electrode. Then, bothelectrodes 1 a and 1 b are covered with the insulator.

Then, as illustrated in FIG. 18, as a capacitance Cs1 between theelectrodes 1 a and 1 b or capacitances Cs2 and Cs3 between eachelectrode 1 a and 1 b and a ground GND change when the isolatorinsulator 2 on the electrodes 1 a and 1 b is touched with a finger, anexistence of a touch with a finger may be detected by detecting thechange in the capacitances with a detection circuit.

A capacitance sensor illustrated in FIG. 20 includes an electrode 6disposed in a mounting hole 5 in an insulator 4. The electrode 6 iscovered with a flexible conductive material 7 spaced a certain distanceaway therefrom. When the conductive material 7 is pressed and flexed, adistance between the conductive material 7 and the electrode 6 isreduced, a capacitance between the conductive material 7 and theelectrode 6 changes, and, by detecting the change in the capacitance bya detection circuit, an existence of a touch with a finger is detected.

In the kind of capacitance sensor illustrated in FIG. 18, by adopting aconfiguration wherein a change in the capacitance Cs1 is detected by thedetection circuit, a change in the capacitance Cs1 due to a touch with afinger is comparatively large and relatively unsusceptible to aparasitic capacitance. Therefore, it is possible to detect the existenceof a touch with a high accuracy. However, since a detection signalsimilar to a detection signal obtained from a touch with a finger may betransmitted even when a water droplet or other conductive materialadheres to the insulator 2, problems such as malfunctions can occur.

Also, in the event of adopting a configuration wherein a change in thecapacitance Cs2 between the electrode 1 a and the ground GND, or thecapacitance Cs3 between the electrode 1 b and the ground GND, isdetected by the detection circuit, such a change in capacitance issusceptible to a parasitic capacitance between each electrode 1 a and 1b and the ground GND, thus reducing detection accuracy.

Therefore, when a configuration with a function of canceling a parasiticcapacitance every time is provided in the detection circuit, and withimproved detection accuracy by a calibration operation is adopted, thereis a problem in that the scale of the detection circuit increases.

As a disclosed technology, a sensor circuit which detects a change in acapacitance between two electrodes is disposed in JP-A-2000-65514.

Also, a humidity sensor which detects humidity by detecting acapacitance changing in accordance with a change in humidity isdisclosed in JP-A-2006-58084.

SUMMARY

According to an aspect of the invention, a capacitance sensor includes afirst charging voltage detector configured to detect a change in avoltage loaded into a first capacitor between an electrode and a groundterminal a second charging voltage detector configured to detect achange in a voltage loaded into a second capacitor among a plurality ofelectrodes and a determiner configured to generate a determinationsignal based on a detection voltage transmitted from each of the firstcharging voltage detector and second charging voltage detector.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a capacitance sensor of an embodiment.

FIG. 2 is a block diagram illustrating a capacitance sensor of a firstembodiment.

FIG. 3 is an explanatory diagram illustrating an operation of acomparator.

FIG. 4 is a circuit diagram illustrating a detection circuit.

FIG. 5 is a timing waveform diagram illustrating an operation of thedetection circuit.

FIG. 6 is a circuit diagram illustrating a circuit which generatescontrol signals.

FIG. 7 is a circuit diagram illustrating a delay circuit.

FIG. 8 is a timing waveform diagram illustrating an operation of thecircuit which generates the control signals.

FIG. 9 is a timing waveform diagram illustrating an operation of acharging voltage detector.

FIG. 10 is a layout diagram illustrating electrodes of a secondembodiment.

FIG. 11 is a circuit diagram illustrating a detection circuit of thesecond embodiment.

FIG. 12 is a timing waveform diagram illustrating an operation of thedetection circuit.

FIG. 13 is a circuit diagram illustrating a detection circuit of a thirdembodiment.

FIG. 14 is a timing waveform diagram illustrating an operation of thedetection circuit of the third embodiment.

FIG. 15 is a circuit diagram illustrating a control signal generationcircuit.

FIG. 16 is a block diagram illustrating a fourth embodiment.

FIG. 17 is a block diagram illustrating a modification example of thefourth embodiment.

FIG. 18 is a perspective view illustrating a capacitance sensoroperation example.

FIG. 19 is a layout diagram illustrating a heretofore known electrodeexample.

FIG. 20 is a sectional view illustrating another heretofore knownelectrode example.

DESCRIPTION OF EMBODIMENTS

Hereafter, a description will be given, in accordance with the drawings,of an embodiment of the invention. FIG. 1 illustrates a principle of acapacitance sensor of the embodiment. Electrodes 11 a and 11 b, beingelectrodes of a touch sensor switch, are configured in the same way asthe electrodes 1 a and 1 b illustrated in FIG. 19. A capacitor (a secondcapacitor) Cs1 is provided between the electrodes 11 a and 11 b, andcapacitors Cs2 and Cs3 are provided respectively between electrode 11 aand a ground GND (a ground terminal) and 11 b and a ground GND.

A first charging voltage detector 12 a, which detects a voltage loadedinto the capacitor (a first capacitor) Cs2 between the electrode 11 aand the ground GND, is coupled to the electrode 11 a, and a secondcharging voltage detector 12 b which detects a voltage loaded into thecapacitor Cs1 between the electrodes 11 a and 11 b is coupled to theelectrode 11 b.

The first charging voltage detector 12 a, on detecting a change in thevoltage loaded into the capacitor Cs2, transmits a detection flag F1 toa determiner 13. Also, the second charging voltage detector 12 b, ondetecting a change in the voltage loaded into the capacitor Cs1,transmits a detection flag F2 to the determiner 13.

When both detection flags F1 and F2 are input, the determiner 13, basedon a logical AND of the detection flags F1 and F2, transmits adetermination signal OUT which indicates that a position over theelectrodes 11 a and 11 b has been touched with a finger.

FIG. 2 illustrates a detailed configuration of the first and secondcharging voltage detectors 12 a and 12 b. The electrodes 11 a and 11 bare coupled to a detection circuit 14. The detection circuit 14 detectsthe voltages loaded into the capacitors Cs1 and Cs2 in a time divisionmanner, and transmits the voltages. Consequently, the detection circuit14 is shared by the first and second charging voltage detectors 12 a and12 b.

A signal Vout output from the detection circuit 14, is transmitted to afilter 16 a through a switch 15 a, and to a filter 16 b through a switch15 b. The filters 16 a and 16 b, being low pass filters, remove a highfrequency component of noise from the output signal Vout.

A signal output from the filter 16 a is input into a comparator (a firstcomparator) 17 a, while a signal output from the filter 16 b is inputinto a comparator (a second comparator) 17 b. As illustrated in FIG. 3,the comparators 17 a and 17 b respectively compare detection voltagesVc2 and Vc1, to be described hereafter, transmitted from the filters 16a and 16 b with thresholds Vth1 and Vth2 (Vth2: a first threshold, andVth1: a second threshold). When the voltage levels of the detectionvoltages Vc1 and Vc2 respectively exceed the thresholds Vth1 and Vth2,the comparators 17 a and 17 b transmit output signals of an H level.

The signals output from the comparators 17 a and 17 b are transmittedrespectively to counters (a first counter and a second counter) 18 a and18 b. The counters 18 a and 18 b carry out a count-up operation everytime the signals output from the comparators 17 a and 17 b reach the Hlevel, and, when a count number reaches a certain number, transmit thedetection flags (a first detection flag and a second detection flag) F1and F2 to the determiner 13.

A description will be given, in accordance with FIG. 4, of a specificconfiguration of the detection circuit 14. A switch (a fourth switch) 19a open/close-controlled by a control signal _(Φ) 4, is coupled to theelectrode 11 a, and supplies a low potential side reference voltage•Vref to the electrode 11 a when conducting. Also, a switch (a thirdswitch) 19 b open/close-controlled by a control signal _(Φ) 3 is coupledto the electrode 11 a, and supplies a high potential side referencevoltage •Vref to the electrode 11 a when conducting. The high potentialside reference voltage •Vref may be made a supply voltage, and the lowpotential side reference voltage •Vref may be made a ground GNDpotential.

A switch (a second switch) 19 c open/close-controlled by a controlsignal _(Φ) 2 is coupled between the electrodes 11 a and 11 b, while aswitch 19 e open/close-controlled by a control signal _(Φ) 5 is coupledbetween the electrode 11 b and a negative side input terminal of anoperational amplifier 20. Then, on the switch 19 c becoming conductive,a short-circuit condition occurs between the electrodes 11 a and 11 b,and furthermore, on the switch 19 e becoming conductive, the electrode11 a is coupled to the negative side input terminal of the operationalamplifier 20.

The electrode 11 b is coupled to the negative side input terminal of theoperational amplifier 20 via the switch 19 e, and a reference voltageVcom is input into a positive side input terminal of the operationalamplifier 20. Also, a feedback capacitor Cf and a switch (a firstswitch) 19 d are coupled between the input and output terminals of theoperational amplifier 20.

The switch 19 d is open/close-controlled by a control signal _(Φ) 1.When the switch 19 d conducts, the switch 19 d is coupled to the inputand output terminals of the operational amplifier 20. In the event thatthere is no offset in the operational amplifier 20, the output signalVout reaches a reference voltage Vcom level.

A description will be given, in accordance with FIG. 5, of an operationof the detection circuit configured as described above. The switches 19a to 19 e become conductive when the control signals _(Φ) 1 to _(Φ) 5reach the H level.

On a detection operation being started, firstly, the control signal _(Φ)2 reaches the H level, and the switch 19 c is rendered conductive.

In this condition, a signal which switches between the H level and an Llevel in a certain period is supplied as the control signal _(Φ) 1, andthe control signal _(Φ) 4 in the same phase as that of the controlsignal _(Φ) 1, and the control signal _(Φ) 5 in a reverse phase as thatof the control signal _(Φ) 1 are also supplied.

Thus, when the control signals _(Φ) 1 and _(Φ) 4 reach the H level, andthe control signal _(Φ) 5 reaching the L level, both terminals of thefeedback capacitor Cf are short-circuited, the feedback capacitor Cf isdischarged, and the output signal Vout reaches the reference voltageVcom. The capacitors Cs2 and Cs1 coupled to the electrode 11 a aredischarged up to a reference voltage •Vref level.

Then, when the control signals φ1 and φ4 reach the L level, and thecontrol signal φ5 reaches the H level, the switches 19 a and 19 b becomenon-conductive, and the switch 19 e becomes conductive. Thus, thedetection voltage Vc2 based on a charge loaded into the capacitor Cs2 istransmitted as the output signal Vout from the operational amplifier 20and, a relationship Vc2·Cs2·Cf·Vref being established, a voltage basedon a ratio of capacitance values of the capacitor Cs2 and the feedbackcapacitor Cf is transmitted. Consequently, as the charge loaded into thecapacitor Cs2 increases, for example, when an insulator on theelectrodes 11 a and 11 b is touched with a finger, the detection voltageVc2 increases.

Then, when the control signals _(Φ) 1, _(Φ) 4 and _(Φ) 5 switch, theoutput signal Vout reaches the reference voltage Vcom. Then, thedetection voltage Vc2, based on the switching of the control signals_(Φ) 1, _(Φ) 4 and _(Φ) 5, is repeatedly transmitted as the outputvoltage Vout.

The detection voltage Vc2 is transmitted to the comparator 17 a throughthe conducting switch 15 a based on the control signal _(Φ) 2 and thefilter 16 a. Then, in the comparator 17 a, as illustrated in FIG. 3, anoutput signal, which reaches the H level in the event that the detectionvoltage Vc2 exceeds the threshold Vth1, is transmitted to the counter 18a. The counter 18 a counts pulse signals transmitted from the comparator17 a and, on counting up to a number of pulses set in advance, transmitsthe detection flag F1 of the H level to the determiner 13.

In the heretofore described kind of operation of detecting the chargeloaded into the capacitor Cs2, since the switch 19 c is conductive, avalue is detected which is a combination of the charge loaded into thecapacitor Cs2 and a charge loaded into the capacitor Cs3 between theelectrode 11 b and the ground GND.

After the detection of the detection voltage Vc2, the control signal_(Φ) 2 reaches the L level, and a shift is made to an operation ofdetecting a charge loaded into the capacitor Cs1. As a timing of thisshift, it is also acceptable to make the shift after the detection flagF1 has been transmitted as described above, or to make the shift after aspecified time.

Upon the control signal _(Φ) 2 reaching the L level, the switch 19 cbecomes non-conductive. In this condition, a signal which switchesbetween the H level and the L level in a certain period is supplied asthe control signal _(Φ) 1. The control signal _(Φ) 3 in the same phaseas that of the control signal _(Φ) 1, the control signal _(Φ) 4 in areverse phase of the control signal _(Φ) 1, and the control signal _(Φ)5 of the H level are supplied.

Thus, upon the control signals _(Φ) 1 and _(Φ) 3 reaching the H level,and the control signal _(Φ) 4 reaching the L level, both end outputs ofthe feedback capacitor Cf are short-circuited, the feedback capacitor Cfis discharged, and the output signal Vout reaches the reference voltageVcom. Also, the capacitors Cs2 and Cs1 are charged up to a referencevoltage •Vref level.

Next, upon the control signals _(Φ) 1 and _(Φ) 3 reaching the L level,and the control signal _(Φ) 4 reaching the H level, the referencevoltage •Vref is supplied and the switch 19 d becomes non-conductive.Thus, the detection voltage Vc1 based on the charge loaded into thecapacitor Cs1 is transmitted as the output signal Vout. With arelationship Vc1=2·Cs1/Cf·Vref being established, a voltage based on aratio of charges loaded into the capacitor Cs1 and feedback capacitor Cfis transmitted. Consequently, as the charge loaded into the capacitorCs1 increases, that is, when the insulator on the electrodes 11 a and 11b is touched with a finger, the detection voltage Vc1 increases.

Then, upon the control signals _(Φ) 1, _(Φ) 3 and _(Φ) 4 switching, theoutput signal Vout reaches the reference voltage Vcom. Then, thedetection voltage Vc1, based on the switching of the control signals_(Φ) 1, _(Φ) 3 and _(Φ) 4, is repeatedly transmitted as the outputsignal Vout.

The detection voltage Vc1, based on a control signal _(Φ) 2 bar which isan inverted signal of the control signal _(Φ) 2, is transmitted to thecomparator 17 b through the conducting switch 15 b and the filter 16 b.Then, with the comparator 17 b, as illustrated in FIG. 3, an outputsignal, which reaches the H level in the event that the detectionvoltage Vc1 exceeds the threshold Vth1, is transmitted to the counter 18b. The counter 18 b counts pulse signals transmitted from the comparator17 b and, on counting up to a number of pulses set in advance, transmitsthe detection flag F2 of the H level to the determiner 13.

In the heretofore described kind of detection operation, since acharging potential of the capacitor Cs2 is greatly affected by parasiticcapacitors Cp1 and Cp2 of the electrodes 11 a and 11 b, an arrangementis adopted such that, by setting the threshold Vth1 of the comparator 17a to low, it is possible to roughly detect an approach of a finger tothe electrodes 11 a and 11 b.

Also, a charging potential of the capacitor Cs1 being less affected bythe parasitic capacitors, the charging potential changes greatly uponbringing a finger to a position between the electrodes 11 a and 11 b.For example, supposing that an area of the electrodes 11 a and 11 b isaround 7 mm by 7 mm, and a film pressure of the insulator covering theelectrodes 11 a and 11 b is around 100 μm, on bringing a finger to theelectrodes 11 a and 11 b, a change in the loaded charge amount of 10 pFmay be obtained. Then, when the finger is 1 mm or more away from theelectrodes 11 a and 11 b, the change in the loaded charge amount becomes1/10 or less because the amount is inversely proportional to thedistance.

Consequently, by setting the threshold Vth1 of the comparator 17 b high,the approach of a finger may be detected with a high accuracy.

Also, by using an elastic insulator to cover the electrodes 11 a and 11b, and by providing a clearance between each electrode 11 a and 11 b andthe insulator and by using a flexible insulator, an amount of change inthe charge loaded into the capacitor Cs1 may be increased, and detectionaccuracy may be improved.

FIG. 6 illustrates a circuit generating the control signals _(Φ) 1, _(Φ)3, _(Φ) 4 and _(Φ) 5 which open and close the switches 19 a, 19 b, and19 d. It may be necessary to open and close the switch 19 d, coupled inparallel to the feedback capacitor Cf, in a condition in which theswitches 19 a and 19 b are rendered conductive, FIG. 6 illustrates acircuit generating the control signals _(Φ) 1, _(Φ) 4 and _(Φ) 5.

An input signal P1, which is a clock signal on a certain frequency, isinput into a first delay circuit 21; and a signal P2, in which the inputsignal P1 is delayed a certain amount of time, is transmitted from thefirst delay circuit 21. The signal P2 is transmitted as the controlsignal _(Φ) 1 through a buffer circuit 23. Consequently, as illustratedin FIG. 8, the control signal _(Φ) 1 is a signal in which the inputsignal P1 is delayed by the first delay circuit 21.

The signal P2 is input into a second delay circuit 22, and a signal P3,in which the signal P2 is delayed a certain amount of time, istransmitted from the second delay circuit 22. Delay times of the firstand second delay circuits 21 and 22 are substantially identical.

The signal P3 is input into an AND circuit 24 a and a NOR circuit 25,and the input signal P1 is input into the AND circuit 24 a and the NORcircuit 25. A signal output from the AND circuit 24 a is input into ANDcircuits 24 b and 24 c, an inverted signal of the control signal _(Φ) 2is input into the AND circuit 24 b, and the control signal _(Φ) 2 isinput into the AND circuit 24 c. Then, the control signal _(Φ) 3 istransmitted from the AND circuit 24 b.

Signals output from the AND circuit 24 c and the NOR circuit 25 areinput into an OR circuit 29 a, and the control signal _(Φ) 4 istransmitted from the OR circuit 29 a.

The signal output from the NOR circuit 25 is input into an OR circuit 29b, and the control signal _(Φ) 2 is input into the OR circuit 29 b.Then, the control signal _(Φ) 5 is transmitted from the OR circuit 29 b.

With the above configuration, the control signals _(Φ) 1, _(Φ) 4 and_(Φ) 5 switch at the timings illustrated in FIG. 8. Consequently, theswitch 19 d is controlled in such a way as to switch between aconductive condition and a non-conductive condition when both switches19 a and 19 b become non-conductive, and the switches 19 a and 19 b arecontrolled in such a way that one becomes non-conductive when the otheris in a switching operation. By this kind of operation, errors due to acharge transfer between the capacitors Cs1, Cs2, and Cs3 in atransitional state of the switches 19 a, 19 b, and 19 d may be reduced.

FIG. 7 illustrates a specific configuration of the first delay circuit21. The second delay circuit 22 also has substantially the sameconfiguration. In each of these delay circuits, six inverter circuits 26a to 26 f are coupled in series, and time constant circuits 27 a and 27b are interposed respectively between the inverter circuits 26 b and 26c, and between the inverter circuits 26 e and 26 f.

Also, an input terminal of the inverter circuit 26 c is coupled to thepower supply VDD via P channel MOS transistors Tp1 and Tp2, and coupledto the ground GND via N channel MOS transistors Tn1 and Tn2. Gates ofthe transistors Tp1 and Tn2 are coupled to an output terminal of theinverter circuit 26 a, and gates of the transistors Tp2 and Tn1 arecoupled to an output terminal of the inverter circuit 26 c.

Also, an input terminal of the inverter circuit 26 f is coupled to thepower supply VDD via P channel MOS transistors Tp3 and Tp4, and coupledto the ground GND via N channel MOS transistors Tn3 and Tn4. Gates ofthe transistors Tp3 and Tn4 are coupled to an output terminal of theinverter circuit 26 d, and gates of the transistors Tp4 and Tn3 arecoupled to an output terminal of the inverter circuit 26 f.

Then, the input signal P1 is input into an input terminal of theinverter circuit 26 a, and a signal output from the inverter circuit 26f is transmitted as the signal P2 through a buffer circuit 28.

With the first delay circuit 21 configured in this way, a delay time isgenerated based on an operation delay time of each inverter circuit 26 ato 26 f and by the time constant circuits 27 a and 27 b, and the signalP2, which is the delayed input signal P1, is transmitted.

When a signal input into the inverter circuit 26 c exceeds a thresholdon a low potential side or a high potential side, the transistors Tp1,Tp2, Tn1, and Tn2, based on a signal output from the inverter circuit 26c, operate in such a way as to swiftly shift a level of the signal inputinto the inverter circuit 26 c to a ground GND level or a power supplyVDD level. The transistors Tp3, Tp4, Tn3, and Tn4 also operate insubstantially the same way.

FIG. 9 illustrates operations of the first and second charging voltagedetectors 12 a and 12 b including the detection circuit 14.

Upon the control signal _(Φ) 2 reaching the H level, an operation ofdetecting the charge loaded into the capacitor Cs2 is started, and thecounter 18 a is reset. Then, with the detection circuit 14, the outputsignal Vout is transmitted by an operation of switching between thecontrol signals _(Φ) 1, _(Φ) 3, and _(Φ) 4. A period of maintaining thecontrol signal _(Φ) 2 at the H level is taken to be, for example, aperiod until a number of pulses of the input control signal _(Φ) 1reaches “n”.

Thus, by the operation of switching between the control signals _(Φ) 1,_(Φ) 3 and _(Φ) 4, the detection voltage Vc2 is transmitted and, uponthe detection voltage Vc2 exceeding the threshold Vth1 of the comparator17 a, pulse signals transmitted from the comparator 17 a are counted bythe counter 18 a. Then, upon a count value reaching a certain number,the detection flag F1 of the H level is transmitted from the counter 18a.

Then, upon the control signal _(Φ) 2 reaching the L level, the operationof detecting the charge loaded into the capacitor Cs1 is started, andthe counter 18 b is reset. Then, with the detection circuit 14, theoutput signal Vout is transmitted by the operation of switching betweenthe control signals _(Φ) 1, _(Φ) 3, and _(Φ) 4. A period of maintainingthe control signal _(Φ) 2 at the L level is taken to be, for example, aperiod until a number of pulses of the input control signal _(Φ) 1reaches “m”.

Thus, by the operation of switching between the control signals _(Φ) 1,_(Φ) 3, and _(Φ) 4, the detection voltage Vc1 is transmitted and, uponthe detection voltage Vc1 exceeding the threshold Vth1 of the comparator17 b, pulse signals transmitted from the comparator 17 b are counted bythe counter 18 b. Then, upon a count value reaching a certain number,the detection flag F2 of the H level is transmitted from the counter 18b.

Then, upon the detection flags F1 and F2 both reaching the H level, adetermination signal OUT indicating that a position between theelectrodes 11 a and 11 b has been touched with a finger is transmittedfrom the determiner 13.

With the heretofore described capacitance sensor, the followingoperating effects may be obtained. 1. Roughly detecting a change in thecharge loaded into the capacitor Cs2 between the electrode 11 a and theground GND by means of the detection circuit 14, then detecting a changein the charge loaded into the capacitor Cs1 between the electrodes 11 aand 11 b, which is easy to detect with a high accuracy, by means of thedetection circuit 14 is possible. Also, based on the results of thedetections, easily determining whether or not a position between theelectrodes 11 a and 11 b has been touched with a finger is possible. 2.Detecting the detection voltage Vc2, which indicates that a change inthe charge loaded into the capacitor Cs2 between the electrode 11 a andthe ground GND has been detected, and detecting the detection voltageVc1, which indicates that a change in the charge loaded into thecapacitor Cs1 between the electrodes 11 a and 11 b has been detected, ina time division manner with the shared detection circuit 14 is possible.Consequently, the scale of the detection circuit 14, which detects thedetection voltages Vc2 and Vc1, may be reduced. 3. By open/closecontrolling the switches 19 a to 19 e with the control signals _(Φ) 1 to_(Φ) 5, detecting the detection voltages Vc2 and Vc1 in a time divisionmanner is possible. 4. Since the switches 19 a, 19 b, 19 d, and 19 e ofthe detection circuit 14 are not simultaneously opened or closed,detection accuracy may be improved. 5. Generating the control signals_(Φ) 1, _(Φ) 3, _(Φ) 4 and _(Φ) 5, which do not allow the switches 19 a,19 b, 19 d, and 19 e to be simultaneously opened or closed is possibleby using the delay circuits 21 and 22, AND circuits 24 a to 24 c, NORcircuit 25, and OR circuits 29 a and 29 b. 6. Pulse signals transmittedfrom the comparators 17 a and 17 b are counted by the counters 18 a and18 b and, when a count number reaches a certain value, the detectionflags F1 and F2 are transmitted. Therefore, erroneous determination dueto noise may be reduced if not prevented.

FIGS. 10 to 12 illustrate a second embodiment. This embodimentillustrates a case of configuring a capacitance sensor that detectswhether any one of three electrodes has been touched.

As illustrated in FIG. 10, three electrodes 31 b to 31 d of asubstantially identical shape is placed side by side, and an electrode31 a is laid out between the electrodes 31 b to 31 d and around eachelectrode 31 b to 31 d. Then, each electrode 31 a to 31 d is coveredwith an insulating material.

FIG. 11 illustrates a detection circuit 32 of the capacitance sensor ofthis embodiment. Components identical to those of the detection circuit14 of the first embodiment will be described using the same referencenumbers and characters.

The electrode 31 a is coupled to the negative side input terminal of anoperational amplifier 20, and a capacitor Cy is provided between theelectrode 31 a and the ground GND.

One terminal of the switch 19 c is coupled to the negative side inputterminal of the operational amplifier 20, and switches 33 a to 33 c arecoupled between the other terminal of the switch 19 c and each electrode31 b to 31 d respectively. The switches 33 a to 33 c, areopen/close-controlled by control signals _(Φ) 6 to _(Φ) 8, and arerendered conductive when the control signals _(Φ) 6 to _(Φ) 8 reach theH level.

Capacitors Cx1, Cx2, and Cx3 are provided between the electrode 31 a andeach electrode 31 b to 31 d, respectively.

FIG. 12 illustrates timing waveforms of the control signals _(Φ) 1 to_(Φ) 8 which open/close-control the switches 19 a to 19 d and 33 a to 33c. Firstly, in a condition in which the control signal _(Φ) 2 is set atthe H level and the switch 19 c is rendered conductive, upon the controlsignals _(Φ) 1 and _(Φ) 4 switching in the same phase in a certainperiod, and the control signal _(Φ) 5 switching in a reverse phase, avoltage loaded into the capacitor Cy between the electrode 31 a and theground GND is detected and transmitted as the output signal Vout.

Then, the control signals _(Φ) 6 to _(Φ) 8 sequentially reach the Hlevel in a condition in which the control signal _(Φ) 2 reaches the Llevel, the switch 19 c becomes non-conductive, the control signals _(Φ)1 and _(Φ) 3 switch in the same phase in the certain period, and thecontrol signal _(Φ) 4 switches in a reverse phase to that of the controlsignals _(Φ) 1 and _(Φ) 3.

Thus, the switches 31 b to 31 c sequentially become conductive, andvoltages loaded into the capacitors Cx1, Cx2, and Cx3 between theelectrode 31 a and each electrode 31 b to 31 d are sequentially detectedand transmitted as the output signals Vout.

By determining, based on the kinds of output signals Vout, whether ornot the voltage loaded into the capacitor Cy has exceeded a certainthreshold, and furthermore, whether or not any one of the voltagesloaded into the capacitors Cx1 Cx2, and Cx3 has exceeded a certainthreshold, which of positions on the electrodes 31 b to 31 d a fingerhas touched may be determined.

For example, in the event that an increase in the voltage loaded intothe capacitor Cx1 is detected following an increase in the voltageloaded into the capacitor Cy, the fact that a position on the electrode31 b has been touched may be detected. Also, in the event that anincrease in the voltage loaded into the capacitor Cx2 is detectedfollowing the increase in the voltage loaded into the capacitor Cy, thefact that a position on the electrode 31 c has been touched may bedetected. In the same way, in the event that an increase in the voltageloaded into the capacitor Cx3 is detected following the increase in thevoltage loaded into the capacitor Cy, the fact that a position on theelectrode 31 c has been touched may be detected.

With this kind of configuration, a capacitance sensor for a touch sensorswitch provided with three touch sensor sections in combination may beconfigured.

FIGS. 13 to 15 illustrate a third embodiment. This embodiment is onewhich configures a detection circuit 14 a in which a function ofcanceling an offset voltage of the operational amplifier 20 is added tothe detection circuit 14 of the first embodiment illustrated in FIG. 4.Components similar to those of the first embodiment will be describedwith the same reference numbers and characters.

A switch 34 a is coupled between the feedback capacitor Cf and theoutput terminal of the operational amplifier 20, and the switch 34 a isopen/close-controlled by the control signal _(Φ) 4.

Also, the reference voltage Vcom is supplied through a switch 34 b to aconnection point between the feedback capacitor Cf and the switch 34 a.The switch 34 b is open/close controlled by the control signal _(Φ) 1.

With this kind of detection circuit 14 a, when the control signal _(Φ) 1reaches the H level, and the switch 19 d becomes conductive, a gain ofthe operational amplifier 20 becomes 1 while, in the event that there isno offset voltage in the operational amplifier 20, the output signalVout reaches the reference voltage Vcom.

Since the switch 34 b also becomes conductive at this time, in the eventthat an offset voltage exists in the operational amplifier 20, thefeedback capacitor Cf is charged with an amount equivalent to the offsetvoltage. Then, the switch 19 d becomes non-conductive and, whendetecting charges loaded into the capacitors Cs2 and Cs1, an outputsignal Vout, which has canceled the offset voltage of the operationalamplifier 20, is transmitted.

Also, the signal Vout output from the operational amplifier 20 may notimmediately reach the reference voltage Vcom even when the controlsignal _(Φ) 1 becomes conductive. This is because it takes time tocharge and discharge a capacitor coupled to the input terminal of theoperational amplifier 20.

When increasing a load drive ability of the operational amplifier 20 inorder to avoid this, power consumption is increased. Also, when reducingthe load drive ability of the operational amplifier 20, a reduction ofthe output signal Vout to the reference voltage Vcom is delayed.

With the detection circuit 14 a, the reference voltage Vcom is suppliedto the input terminal of the operational amplifier 20 through the switch34 c which is open/close-controlled by the control signal _(Φ) 6.

The control signal _(Φ) 6 is generated from the control signal _(Φ) 1 bythe generation circuit illustrated in FIG. 15. That is, the controlsignal _(Φ) 1 is input into a delay circuit 35, and a signal output fromthe delay circuit 35 is input into an AND circuit 37 through an invertercircuit 36. Also, the control signal _(Φ) 1 is input into the ANDcircuit 37, and the control signal _(Φ) 6 is transmitted from the ANDcircuit 37.

As illustrated in FIG. 14, the control signal _(Φ) 6 rises along with arise of the control signal _(Φ) 1, reaches the H level and, after adelay time set by the delay circuit 35, returns to the L level prior tothe fall of the control signal _(Φ) 1.

Consequently, upon the control signal _(Φ) 1 reaching the H level, andthe switch 19 d becoming conductive, the control signal _(Φ) 6 alsoreaches the H level, the switch 34 c becomes conductive, and the inputterminal of the operational amplifier 20 swiftly reaches the referencevoltage Vcom level. As a result, as illustrated in FIG. 14, the signalVout output from the operational amplifier 20 swiftly reaches thereference voltage Vcom level.

With the detection circuit 14 a configured as described above, thefollowing operational effects may be obtained. 1. The offset voltage ofthe operational amplifier 20 may be cancelled. 2. When the output signalVout is reset to the reference voltage Vcom, the reset operation may besped up.

FIG. 16 illustrates a fourth embodiment. This embodiment is one which isarranged in such a way that the operations of the comparators 17 a and17 b, counters 18 a and 18 b, and determiner 13 of the first embodimentare carried out by a microcomputer 38. Components similar to those ofthe first embodiment will be described with the same reference numbersand characters.

The detection voltages Vc2 and Vc1 transmitted from the filters 16 a and16 b are input into the microcomputer 38 through amplifiers 39 a and 39b, respectively. The microcomputer 38 converts analog signals input fromthe amplifiers 39 a and 39 b into digital signals by an A/D converter,determines based on the digital signals whether or not the detectionvoltages Vc2 and Vc1 exceed a certain threshold, and detects whether ornot the electrode 11 a has been touched with a finger.

With this kind of configuration, with an apparatus furnished with themicrocomputer 38, a detection signal from the capacitance sensor may bedetermined without providing the comparators 17 a and 17 b, counters 18a and 18 b, or determiner 13 of the first embodiment.

FIG. 17 illustrates a configuration such that, by controlling anoperation of detecting the detection voltages Vc2 and Vc1 in thedetection circuit 14, based on a control signal _(Φ)x transmitted fromthe microcomputer 38, the detection voltages Vc2 and Vc1 are transmittedto the microcomputer 38 through a shared filter 40 and amplifier 41.

With this kind of configuration, sharing the filter 40 and amplifier 41,and reducing a circuit scale of the capacitance sensor in comparisonwith the configuration illustrated in FIG. 16 is possible.

The heretofore described embodiments can be implemented in a mannerillustrated hereafter. Since a change in the charge loaded into thecapacitor Cs1 between the electrodes 11 a and 11 b can be detected witha high accuracy in the first embodiment, signals output from thecomparator 17 b may be input into the determiner 13 as the detectionflag F2.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A capacitance sensor comprising: a first charging voltage detectorconfigured to detect a change in a voltage loaded into a first capacitorbetween a first electrode and a ground terminal; a second chargingvoltage detector configured to detect a change in a voltage loaded intoa second capacitor between the first electrode and a second electrode;and a determiner configured to generate a determination signal based ona detection voltage transmitted from each of the first charging voltagedetector and second charging voltage detector, wherein the firstcharging voltage detector includes: a first comparator configured tocompare a first detection voltage obtained from the first detectionoperation of the detection circuit with a first threshold; a firstcounter configured to count an output from the first comparator, thesecond charging voltage detector includes: a second comparatorconfigured to compare a second detection voltage obtained from thesecond detection operation of the detection circuit with a secondthreshold; a second counter configured to count an output from thesecond comparator, wherein the determiner is configured to output thedetermination signal when detecting an output of the first counter andan output of the second counter.
 2. The capacitance sensor according toclaim 1, wherein the first charging voltage detector includes adetection circuit configured to detect the voltage loaded into the firstcapacitor, and the second charging voltage detector includes a detectioncircuit configured to detect the charge in voltage loaded into thesecond capacitor, wherein a first detection operation configured todetect the charge in voltage loaded into the first capacitor, and asecond detection operation configured to detect the charge in voltageloaded into the second capacitor, are carried out in a time divisionmanner by a shared detection circuit.
 3. The capacitance sensoraccording to claim 2, wherein the shared detection circuit includes: anoperational amplifier having an output terminal and an input terminalcoupled one of the first capacitor and second capacitor selectively; anda first switch coupled between the input terminal and the outputterminal, wherein when the first switch becomes conductive, a lowpotential side reference voltage is supplied to the first and secondcapacitors, when the first switch becomes non-conductive, a highpotential side reference voltage is supplied to the first and secondcapacitors.
 4. The capacitance sensor according to claim 3, furthercomprising: a generation circuit configured to generate a control signalwhich open/close-controls each of the first to fourth switches and,after rendering the third switch non-conductive, renders the firstswitch conductive, then renders the fourth switch conductive.
 5. Thecapacitance sensor according to claim 3, further comprising: a switchconfigured to couple a plurality of third capacitors between a pluralityof third electrodes to the operational amplifier.
 6. The capacitancesensor according to claim 3, further comprising: a switch configured to,when the first switch conducts, supply a reference voltage to be inputinto the operational amplifier to the output terminal of the operationalamplifier.
 7. The capacitance sensor according to claim 3, wherein thereference voltage is supplied to the input terminal of the operationalamplifier through a switch which becomes conductive concurrently withthe first switch, and becomes non-conductive prior to the first switchbecoming non-conductive.
 8. The capacitance sensor according to claim 3,wherein the determiner is a microcomputer which A/D converts thedetection voltages transmitted from the first and second chargingvoltage detectors into digital signals and, based on the digitalsignals, generates the determination signal.
 9. The capacitance sensoraccording to claim 3, wherein the shared detection circuit furtherincludes: a feedback capacitor provided between the input terminal andthe output terminal; a second switch configured to select one of thefirst capacitor and second capacitor to be coupled to the input terminalof the operational amplifier; a third switch configured to, whenconducting, supply the low potential side reference voltage to the firstcapacitor and the second capacitor; and a fourth switch configured to,when conducting, supply the high potential side reference voltage to thefirst capacitor and the second capacitor, wherein the signal output fromthe operational amplifier is reset when the first switch becomesconductive.
 10. The capacitance sensor according to claim 1, wherein thefirst comparator, when the first detection voltage exceeds the firstthreshold, transmits an output signal having a first level; and thefirst counter configured to transmit a first detection flag based on acount value, the second comparator, when the second detection voltageexceeds the second threshold, to transmit an output signal having afirst level; and the second counter configured to transmit a seconddetection flag based on a count value, and wherein the determinergenerates the determination signal based on the first and seconddetection flags.
 11. The capacitance sensor according to claim 10,wherein the second threshold is set at a voltage higher than the firstthreshold.
 12. The capacitance sensor according to claim 1, wherein thesecond electrode is connected to a third capacitor connected between thesecond electrode and the ground terminal.
 13. The capacitance sensoraccording to claim 1, wherein the first electrode and the secondelectrode are disposed under a touch surface.
 14. The capacitance sensoraccording to claim 1, wherein the capacitance sensor is a touch sensor.15. A capacitance sensor comprising: a first charging voltage detectorconfigured to detect a change in a voltage loaded into a first capacitorbetween a first electrode and a ground terminal; a second chargingvoltage detector configured to detect a change in a voltage loaded intoa second capacitor between the first electrode and a second electrode;and a determiner configured to generate a determination signal based ona detection voltage transmitted from each of the first charging voltagedetector and second charging voltage detector, wherein the firstcharging voltage detector includes a detection circuit configured todetect the voltage loaded into the first capacitor, and the secondcharging voltage detector includes a detection circuit configured todetect the charge in voltage loaded into the second capacitor, wherein afirst detection operation configured to detect the charge in voltageloaded into the first capacitor, and a second detection operationconfigured to detect the charge in voltage loaded into the secondcapacitor, are carried out in a time division manner by a shareddetection circuit, wherein the shared detection circuit includes: anoperational amplifier having an output terminal and an input terminalcoupled one of the first capacitor and second capacitor selectively; anda first switch coupled between the input terminal and the outputterminal, wherein, when the first switch becomes conductive, a lowpotential side reference voltage is supplied to the first and secondcapacitors and, when the first switch becomes non-conductive, a highpotential side reference voltage is supplied to the first and secondcapacitors.
 16. The capacitance sensor according to claim 15, whereinthe shared detection circuit further includes: a feedback capacitorprovided between the input terminal and the output terminal; a secondswitch configured to select one of the first capacitor and secondcapacitor to be coupled to the input terminal of the operationalamplifier; a third switch configured to, when conducting, supply the lowpotential side reference voltage to the first capacitor and the secondcapacitor; and a fourth switch configured to, when conducting, supplythe high potential side reference voltage to the first capacitor and thesecond capacitor, wherein the signal output from the operationalamplifier is reset when the first switch becomes conductive.